1. Field of the Invention
The invention relates to an antenna system for motor vehicles, in particular for the reception of television and radio broadcasts and for the data transfer via geo-stationary satellites in the frequency range greater than 10 Ghz.
2. The Prior Art
For antennas for receiving transmissions from geo-stationary satellites, the elevation angle in central Europe lies at 30 degrees. Known and customarily employed satellite receiving antennas are the parabolic mirror antennas and, to a lesser extent, the planar antennas. Now, if one wanted to arrange somewhere on the body of a motor vehicle a parabolic mirror antenna with the geometry and size required for adequate gain, this would not be accepted according to current design ideas and for aerodynamic reasons.
Planar antennas are more compact; however, they are just as little suitable with their radiation lobes disposed orthogonally relative to the aperture as well. If one were to integrate a planar antenna, for example in a horizontal position in the roof of a vehicle, the direction of radiation would be wrong. If one would position it with the correct elevation, one would have the same problems as with the parabolic mirror antennas.
In addition, an antenna with directional characteristic arranged in or on the vehicle is also required to continually react to changes in the direction of radiation in accordance with the constant changes in direction occurring when the vehicle is in operation.
Antennas with directional characteristic are known from the field of radar technology where an omnidirectional radiation effect is achieved by cintinuously rotating the emitter or reflector. Such antennas combine the high, or at least adequate gain achievable with the directional effect, with an azimuth scanning of 360 degrees. The antenna, in most cases a parabolic mirror antenna, is rotated with mechanical means with a constant speed and direction.
However, said principle is not suitable for motor vehicles, in particular not for passenger cars because of the form in which the antenna is constructed. Furthermore, one needs to think of the relatively high rotational speeds at which the system would have to rotate for satellite reception, as well as of the expenditure connected therewith.
In central Europe, the reception of signals from geostationary satellites by the motor vehicle has been possible heretofore only by parking the vehicle and then extending or setting up a satellite antenna of the described type and then aligning it like a stationary antenna by hand or automatically depending on the degree of comfort offered by the equipment. This is customarily done, for example in connection with recreational motor vehicles (RV's).